There are several different technologies that may rely on accurate synchronisation of clocks for proper operation. For example, TDD (time division duplex) in a cellular network is a radio technology that may rely on alignment between clocks of adjacent base stations in the cellular network. CDMA (Code Division Multiple Access) is an example of such radio technology.
There are existing approaches to synchronising clocks over a network. One approach is NTP (Network Time Protocol), which is a protocol for synchronising clocks of computer systems over packet-switched networks. However, in some applications the accuracy achieved using NTP is inadequate.
An alternative approach that offers greater accuracy than NTP is GPS (Global Positioning System) technology. By using GPS technology, each clock can receive timing information based on signals received from satellites orbiting the Earth. Thus, GPS technology can enable accurate synchronisation of clocks in a manner that bypasses any need for signalling through a network.
Unfortunately, in order to use GPS technology for synchronising clocks, a GPS receiver may be implemented with each clock. The cost involved in having the GPS receivers can be significant, especially if there are several clocks to be synchronised. Moreover, if any clocks are located where there is no line of sight to receive the signals from the satellites, then the GPS technology may not even be a workable solution.
Another approach is PTP (Precision Time Protocol) as recently revised in IEEE 1588™-20081. By using this revision of PTP, it may be possible to synchronise distributed clocks with an accuracy of less than one microsecond via Ethernet networks. 1 IEEE Instrumentation and Measurement Society. IEEE Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control Systems. New York: IEEE, 2008